A silver halide photographic material usually comprises a silver halide emulsion layer provided on a plastic support. The plastic support is made of a cellulose derivative (e.g., triacetylcellulose) or a polyester (e.g., polyethylene terephthalate, polyethylene naphthalate).
Plastic tends to be charged due to rubbing because plastic is a non-conductive material. If a photographic material is charged, an electric discharge makes a static mark on an image. Further, the charged material gathers dust. Therefore, an electroconductive layer, namely an antistatic layer is provided on a photographic material having a plastic support to prevent the static charge. The anitistatic layer is usually provided on the backing surface of the plastic support.
The antistatic backing layer of the photographic material is described in Japanese Patent Provisional Publication Nos. 49(1974)-121523, 51(1976)-30725, 55(1980)-70837, 55(1980)-95942 and 57(1982)-118242.
The antistatic backing layer contains electroconductive particles and a binder. In the process for the preparation of the photographic material, an aqueous coating solution containing the particles and the binder is coated on the plastic support to form the antistatic layer. However, the plastic support repels the aqueous solution because the affinity between the plastic and the solution is low. Accordingly, the antistatic layer does not sufficiently adhere to the plastic support. Further, it is difficult to form the anitistatic layer uniformly and smoothly on the support. The antistatic layer tends to be peeled from the plastic support where the adhesion between the layer and the support is insufficient. Further, a printed image is distorted where the antistatic layer is not uniformly formed. Furthermore, a static mark is made in the image where the layer is not smoothly formed.
Various means have been proposed to solve the above-mentioned problems.
The surface of the plastic support can be subjected to a hydrophilic treatment to increase the affinity between the support and the aqueous coating solution. The hydrophilic treatments include a glow discharge treatment, an ultraviolet irradiation treatment and a corona discharge treatment. For example, U.S. Pat. No. 5,326,689 (Murayama) discloses a silver halide photographic material having a polyester support, which is subjected to a glow discharge treatment. However, the affinity between the treated support and the coating solution is still insufficient.
A surface active agent (a coating aid) can be added to the aqueous coating solution to increase the affinity. In Example 1 of U.S. Pat. No. 5,326,689 (at column 22), polyoxyethylene nonylphenylether is added to the coating solution of the antistatic backing layer. The polyoxyethylene (i.e., polyethylene glycol) surface active agent is commonly used in a silver halide photographic material. However, the affinity between the support and the coating solution containing the polyoxyethylene surface active agent is still insufficient.
Further, the common polyoxyethylene surface active agent causes another problem on a silver halide emulsion layer. A process for the preparation of the photographic material often comprises the steps in order of forming the antistatic backing layer on one side of the support, winding the support on a roll, and then forming the emulsion layer on the other side of the support. The common polyoxyethylene surface active agent in the antistatic layer is transferred to the other side of the support when the support is wound on the roll. The transferred surface active agent decreases the adhesion between the support and the layer provided on the side, such as a silver halide emulsion layer. Further, the common polyoxyethylene surface active agent decreases the adhesion between the antistatic backing layer and another backing layer provided on the antistatic layer.
The problems can be solved by using a hydrophobic organic solvent in place of water in the coating solution. However, the organic solvent has problems about danger of explosion. Further, the evaporated solvent should be evacuated. Therefore, an aqueous coating solution is preferred to the hydrophobic solution. The problems should be solved by improving the aqueous coating solution.